You can reach the dealer, I think there should be some spare parts for ZENMUSE.
What happened with yours?
I understand the length of GH3 HDMI cable is different from GH2.
I had the experience that you can loose some screws in the HDMI board and then you can easily to unplug the HDMI cable easily.
However, the cable is easy to get damaged, so you must be very careful.